Deactivating a Tech - is there any documentation on when you do this?

I've been searching for some documentation that tells me all about deactiving a tech, but haven't had any luck finding one.  We have a tech that is no longer with us and I have made his account in active, i'm just wondering  what happens to their old OPEN tickets - who do they get assigned to, how do you do a search for their closed tickets, etc?